Born Approximation Multi-Resolution Imaging for TEM Pseudo Wavefield Based on Differential Pulse

In this study, to obtain Born approximation multi-resolution imaging for transient electromagnetic (TEM) pseudo wavefield, employing a series of differential pulse with multiple pulse widths as the transmission waveform. First, the spectral characteristics of square wave and differential pulse are compared, and the results reveal that differential pulse, compared to the square wave, can effectively eliminate low-frequency interference while maintaining more concentrated distribution of harmonic components. Second, the relationship between pulse width of differential pulse and detection depth is discussed, the findings indicate that the differential pulse with varying pulse widths exhibits different dominant frequency, corresponding to different exploration depths. Then, using two-layer and four-layer models for the method validation, it is evident that the differential pulse with varying pulse widths effectively captures geological information at different depths. At last, through calculations of a 3D model containing low-resistivity bodies and a thrust fault model, the results suggest that correlatively stacking imaging results of differential pulse with varying pulse widths can effectively provide subsurface interface information, spanning from shallow to deep layers. In general, the Born approximation multi-resolution imaging method based on differential pulse plays a significant role in interpreting the TEM pseudo wavefield data.